Given that you can't toss a rock in Vegas without hitting some nouveau cirqus act, it is no surprise that Cirque du Soleil's 'O' takes our trippers choice as best show in Vegas. Considered to be the best show in Vegas by many, with some even daring to say best in the world, it is no wonder that O swept this category. Fire and water provide the backdrop to the 'Cirque-ified' street theatre. With a 1.5 million gallon tank, they out water Le Reve by 50%. Does more water = more fun? You betcha, in this case.